1. Field of the Invention
The present invention relates to a printhead, a printing apparatus, and a printhead driving method and, more particularly, to a printhead which is provided with heaters in correspondence with discharge orifices that discharge ink and discharges ink by heating the heaters, a thermal inkjet printing apparatus using the printhead, and a driving method for the printhead.
2. Description of the Related Art
Conventional inkjet printing apparatuses form images by discharging small ink droplets onto the surfaces of print media. In recent years, various print media are printed using inks of a plurality of colors such as black (Bk), cyan (C), magenta (M), and yellow (Y). In particular, a thermal inkjet printing apparatus can finely control the ink discharge amount by controlling the amount of energy supplied to heaters provided in correspondence with discharge orifices. An inkjet printing apparatus has also been known, which changes the amount of energy supplied to the heaters in accordance with the temperature of the printhead or ink.
The temperature of a thermal printhead rises upon a continuous print operation. As the temperature of the printhead or ink changes, the ink discharge amount upon supplying the same amount of energy to the heaters changes. For this reason, most of the inkjet printing apparatuses control to maintain the printheads at high temperatures in advance by heating the printheads as their temperatures drop. The discharge and non-discharge of inks from the printheads are controlled on demand. Under the circumstance, Japanese Patent Laid-Open No. 6-328722, for example, discloses an inkjet printing apparatus which applies, to an electrothermal transducer (heater) which does not discharge ink in printing, energy in an amount that does not allow it to discharge ink.
However, the inkjet printing apparatus disclosed in Japanese Patent Laid-Open No. 6-328722 described above requires a separate circuit to apply, to a heater which does not discharge ink, energy in an amount that does not allow it to discharge ink, so the circuitry in the inkjet printing apparatus is complicated. In addition, the number of electrical wiring lines from a data control unit of the inkjet printing apparatus to the printhead increases. For example, note that the main board mounting the data control unit of the inkjet printing apparatus and the printhead are connected via a cable. The larger the number of electrical wiring lines, the larger the sizes of the cable and connector, resulting in increases in apparatus size and cost. Furthermore, printhead temperature control cannot be done independently of ink discharge control.